The drug is the most potent diuretic:

Correct Answer: A

Rationale: The correct answer is A: Loop diuretics. Loop diuretics are the most potent diuretics because they act on the thick ascending limb of the loop of Henle, where they inhibit sodium and chloride reabsorption, leading to significant diuresis. This mechanism results in a higher diuretic effect compared to other classes of diuretics. Thiazide diuretics (B) act on the distal convoluted tubule and are less potent. Potassium-sparing diuretics (C) work on the collecting duct and have a weaker diuretic effect. Carbonic anhydrase inhibitors (D) work on the proximal tubule and are considered mild diuretics compared to loop diuretics.

Correct Answer: B

Rationale: Step 1: Quinolone derivatives are a class of antibiotics that target bacterial DNA synthesis. Step 2: Nalidixic acid is a first-generation quinolone derivative that inhibits DNA gyrase enzyme. Step 3: Nalidixic acid is effective against gram-negative bacteria, making it an antibacterial drug. Step 4: Nitrofurantoin is a nitrofuran antibiotic, not a quinolone derivative. Step 5: Streptomycin is an aminoglycoside antibiotic that inhibits protein synthesis, not DNA synthesis. Step 6: Metronidazole is an antimicrobial drug used for anaerobic bacteria and protozoa, not a quinolone derivative.

Correct Answer: C

Rationale: Step-by-step rationale: 1. Saquinavir is a protease inhibitor used in the treatment of HIV by blocking viral proteases essential for viral replication. 2. Rimantadine is an antiviral drug used for influenza A virus, not inhibiting viral proteases. 3. Acyclovir is an antiviral drug for herpes simplex virus, working by inhibiting viral DNA synthesis, not proteases. 4. Zalcitabine is a nucleoside analog used for HIV, but it inhibits reverse transcriptase, not viral proteases. Summary: Saquinavir is the correct answer as it specifically inhibits viral proteases crucial for viral replication. The other choices target different viral enzymes or processes, making them incorrect for this question.

Correct Answer: C

Rationale: The correct answer is C: Nitroglycerin. Nitroglycerin is a vasodilator that works by releasing nitric oxide, which leads to decreased platelet aggregation. This helps improve blood flow and reduce symptoms like chest pain in patients with heart conditions. Propranolol (A) is a beta-blocker that doesn't directly affect platelet aggregation. Isosorbide mononitrate (B) is a vasodilator but doesn't have a significant impact on platelet aggregation. Nifedipine (D) is a calcium channel blocker that also doesn't directly influence platelet aggregation.

Correct Answer: A

Rationale: The correct answer is A: Severe postural hypotension. Adding a third drug that decreases central sympathetic outflow (possibly a centrally acting alpha-2 adrenergic agonist) can lead to a sudden drop in blood pressure upon standing, causing postural hypotension. This occurs due to decreased sympathetic tone leading to vasodilation and reduced vascular tone. This effect is more likely to occur shortly after initiating therapy with the new drug. Choice B: Megaloblastic anemia is not a common adverse effect of drugs that decrease sympathetic outflow. Choice C: Palpitations are not typically associated with drugs that decrease sympathetic outflow. Choice D: Pronounced sedation is not a common side effect of centrally acting sympatholytic drugs.